E. E. Lekht

Long-term monitoring of the W44C (G 34.3+0.15) maser in the 1.35 cm water vapor and 18 cm hydroxyl lines

Results of monitoring the H2O and OH masers in W44C, located near the cometary HII region G34.3+0.15, are reported. Observations in the water-vapor line at λ = 1.35 cm were carried out on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from November 1979 to March 2011, and in the hydroxyl lines at λ = 18 cm on the large Nançay radio telescope (France). Activity maxima and minima of the water maser alternated. The average period of the activity is ∼ 14 years, consistent with results obtained earlier for a number of other sources associated with regions of active star formation. In periods of enhanced maser activity, two series of strong H2O maser flares were observed, which were related to two different clusters of maser spots located at the front of a shock at the periphery of the ultracompact region UH II. These series of flares may be associated with cyclic activity of the protostellar object in UH II. In the remaining time intervals, there were mainly short-lived flares of single features. The Stokes parameters for the observations in the hydroxyl lines were determined. Zeeman splitting was observed in the profile of the 1667 MHz OH main line at a velocity of 58.5 km/s, and was used to estimate the intensity of the line-of-sight component of the magnetic field (1.2 mG).

The source of maser emission in W33C (G12.8-0.2)

The results of observations of the H2O and OH maser sources toward the region of W33C (G12.8-0.2) are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in the 1.35-cm water-vapor line and on the Large Radio Telescope at Nançay (France), in the main (1665 and 1667 MHz) and satellite (1612 and 1720 MHz) OH lines. Multiple, strongly variable, short-lived H2O emission features were detected in a broad interval of radial velocities, from −7 to 55 km/s. OH maser emission in the 1667-MHz line was detected at velocities of 35–41 km/s. The Stokes parameters of the maser emission in the main OH lines 1665 and 1667 MHz were measured. Zeeman splitting was detected in the 1665-MHz line at 33.4 and 39.4 km/s, and in the 1667 MHz line only at 39.4 km/s. The magnetic-field intensity was estimated. Appreciable variability of the Zeeman splitting components was observed at 39 and 39.8 km/s in both main lines. The extended spectrum and fast variability of the H2O maser emission, together with the variability of the Zeeman-splitting components in the main OH lines, may indicate a composite clumpy structure of the molecular cloud and the presence of large-scale rotation, bipolar outflows, and turbulent motions of material in this cloud.

Results of a long-term monitoring of the 1.35-cm water-vapor maser source ON 1 (1981–2013)

We present the results of our long-term monitoring of the 1.35-cm water-vapor maser source ON 1 performed at the 22-m radio telescope of the Pushchino Radio Astronomy Observatory from 1981 to 2013. Maser emissionwas observed in a wide range of radial velocities, from −60 to +60 km s−1. Variability of the integrated flux with a period of ∼9 years was detected. We show that the stable emission at radial velocities of 10.3, 14.7, and 16.5 km s−1 belongs to compact structures that are composed of maser spots with close radial velocities and that are members of two water-maser clusters, WMC 1 and WMC 2. The detected short-lived emission features in the velocity ranges from −30 to 0 and from 35 to 40 km s−1 as well as the high-velocity ones are most likely associated with a bipolar molecular outflow observed in the CO line.

The H2O maser toward IRAS 06308+0402

We present the monitoring results for the H2O maser toward the infrared source IRAS 06308+0402 associated with a dense cold molecular cloud. The observations were carried out with the 22-m radio telescope at the Pushchino Radio Astronomy Observatory (Russia) during 1992–2003. The H2O maser was discovered in May 1992 (Pashchenko 1992) during a survey of IRAS sources associated with dense cold clouds with bipolar molecular outflows. The H2O spectrum contains many emission features, suggesting the fragmentation of the envelope around a young star. The star has a low peculiar velocity relative to the CO molecular cloud (∼2.2 km s−1). We found a cyclic variability of the total maser flux with a period from 1.8 to 3.1 yr.

H2O and OH masers associated with cold infrared sources

We present the results of our monitoring of four maser sources associated with cold infrared sources. The observations were performed in the water-vapor line at 1.35 cm with the 22-m radio telescope at the Pushchino Radio Astronomy Observatory and in the hydroxyl lines at 18 cm with the Nançay radio telescope. Cyclic variability of the H2O maser emission was detected in all four sources. The durations of the cycles are different and lie within the range 1.8–5.5 yr. In each source, the cycles differed by a factor from 1.5 to 2.25. A fairly periodic pattern of variability was observed in IRAS 20126+4104 on a time scale from 3.6 to 5.3 yr. Models of the maser sources are discussed. In IRAS 20126+4104, we detected strong variability of the maser emission in the main OH 1665 and 1667 MHz lines. We calculated the magnetic field strength for two maser features from the Zeeman splitting of the OH line: in IRAS 18265-1517 (1.3 mG at epoch 2008) and IRAS 20126+4104 (10 mG at epoch 2014). Variability of the magnetic field was detected in the second feature. In the same sources, we detected maser emission in the 1667 MHz OH line. The presence of emission in both main OH 1665 and 1667 MHz lines is consistent with the existing model calculations and will allow the gas density in the masing regions to be refined.

On a new cluster of H2O maser spots in the source ON2

We present the results of our observations of the H2O maser emission toward the complex source ON2 associated with an active star-forming region. The observations were performed in a wide range of radial velocities, from −75 to 90 km s−1. We have detected an emission with flux densities of 9.2, 4, and 26 Jy at radial velocities of −33.5, −24.4, and −18.8 km s−1, respectively, at which no emission has been observed previously. The detected emission is most likely associated with a hitherto unknown cluster of maser spots located between the northern (N) and southern (S) components of the source ON2 (closer to the northern one). This cluster may be associated with one of the three CO molecular outflows in the ON2 region. We have also detected an emission at −22 and −14.5 km s−1 in N and at 12.6 km s−1 in S, which has extended significantly the velocity ranges of the maser emission in these sources and allowed their models to be improved.

Triplet structure of the H2O spectra in S255

We analyzed the monitoring data for the maser S255 obtained in the H2O line at λ=1.35 cm with the 22-m radio telescope at the Pushchino Radio Astronomy Observatory in 1981–2002. The maser was most active during 1998–2002. Since 2001, the H2O spectra have been extended and complex; their triplet structure has been disrupted. The extent of the spectra was 24 km s−1 (from −6 to 18 km s−1). We calculated orbital parameters for some of the components. We estimated the mass of the central star to be (6–7)M⊙ and the outer Keplerian-disk radius to be ∼160 AU.

Investigation of OH and H2O masers in the star-forming region G 188.946+0.886

We present the results of our observations of the maser radio emission source G188.946+0.886 in hydroxyl (OH) molecular lines with the radio telescope of the Nançay Observatory (France) and in the H2O line at λ = 1.35 cm with the RT-22 radio telescope at the Pushchino Observatory (Russia). An emission feature in the 1720-MHz satellite line of the OH ground state has been detected for the first time. The radial velocity of the feature, VLSR = 3.6 km s−1, has a “blue” shift relative to the range of emission velocities in the main 1665- and 1667-MHz OH lines, which is 8–11 km s−1. This suggests a probable connection of the observed feature in the 1720-MHz line with the “blue” wing of the bipolar outflow observed in this region in the CO line. We have estimated the magnetic field strength for three features (0.90 and 0.8 mG for 1665 MHz and 0.25 mG for 1720 MHz) from the Zeeman splitting in the 1665- and 1720-MHz lines. No emission and (or) absorption has been detected in the other 1612-MHz satellite OH line. Three cycles of H2O maser activity have been revealed. The variability is quasi-periodic in pattern. There is a general tendency for the maser activity to decrease. Some clusters of H2O maser spots can form organized structures, for example, chains and other forms.

H2O maser flares in the source W75 N

We present the results of our study of the H2O maser emission in the intricate complex of active star formationW75 N.Our observations have been carried out at the 22-m radio telescope of the Pushchino Radio AstronomyObservatory. A possible identification of its flares with the sources VLA 1 and VLA 2 has been made. Two cycles of maser activity have been detected: 2006–2012 and 2012–2015. The main H2O maser flares occurred in VLA 1. Analysis of the evolution of the flares has shown that the flare emission is associated with a cluster of maser condensations with close radial velocities up to ~2 AU in extent. The medium in which the maser emission is generated is turbulent with various turbulence scales. Our investigation of the line shape at the epochs of flare maxima has also shown the absence of structures of the simplest form, homogeneous maser condensations. The emission in the velocity range from −10.5 to −12 km s−1 has been identified with a structure like an elongated filament with an extent of ~4 AU.

Evolution of the H2O maser emission in IRAS 20126+4104

We present the results of our investigation of the H2O maser emission from individual features in IRAS 20126+4104, which is a cold infrared source. The observations were performed at the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. A radial-velocity drift of the features caused by their deceleration at the interface between between an accelerated jet and the surrounding molecular environment has been detected. The observed tendency for the H2O emission as a whole to drift is associated with the successive excitation of maser features or their clusters by the front of a shock (or magnetohydrodynamic) wave. An estimate of the jet rotation period is provided (∼150 years).